QUAIL

to lose courage, turn frightened

/draw back, as with fear or pain
SYN - cringe, flinch, funk, recoil, shrink, squinch, wince

"He had attacked the problem with so much pluck, but had now quailed and was running back into his mother's arms."

"He should have known that every time he would quail she lost a little more respect for him."

"It was in crucial moments like this that he must remain pluck and not quail."